All done, and to my utter astonishment works 100%.
The Autoleads PC99-213 is a faff, you have to chop the control stalk connector about to get the flying lead into it and then the Autoleads ISO jumper performs the pin swap that I had already done so I had to put it back again, but it's supplied with an uncrimped wire to go find your own switched live when there is a perfectly good one in the Pug ISO. I used the spare electric aerial crimp to patch in.

Nice! Glad you got it all going The stalk is a simple resistor network: each button activates a different resistor (see component "8413" at the bottom of the first diagram on http://406oc.co.uk/viewtopic.php?f=3&t= ... 11#p246711). Seems like the Sony radio understands this "out of the box" so the only thing needed is the correct wiring.

frog wrote: Seems like the Sony radio understands this "out of the box" so the only thing needed is the correct wiring.

The Autoleads kit includes a powered interface box which could well be packed with a quad core processor to interpret and re-code signals appropriately,
or an empty box with wires in.
It is powered though.